1. Field of the Invention
The present invention relates in general to apparatus for controlling the application and removal of an AC voltage to an energy consuming device. More particularly, it relates to apparatus for controlling a system of the type which regulates the temperature in a space for the purpose of reducing the energy consumption thereof.
2. Description of the Prior Art
In recent years, with the increased emphasis on energy conservation, it has become more important to minimize consumption of energy in all facets of daily life. In particular, great improvements in efficiency can be realized in the heating and cooling of buildings.
Although the present invention is applicable to the control of various energy consuming devices, it has been found to be particularly useful in the control of the gas valve of a furnace. Therefore, without limiting the applicability of the invention to "gas valves for furnaces", the invention will be described in this environment.
In a temperature-control unit such as a conventional heating system of the type found in a home, office or warehouse, the heater or furnace portion includes a gas burner having a gas valve which is actuated in response to a thermostat located in an area to be heated. When the temperature detected by the thermostat is below a selected setting, the thermostat signals the gas valve to open, thereby allowing gas to flow into the gas burner where the gas is ignited by the pilot flame. Heat from the gas burner is used to heat a heat exchanger. A fan is turned on when a predetermined temperature is reached in the plenum chamber of the furnace and air is passed over the heat exchanger and distributed throughout the area to be heated via a duct system.
After a brief period of time, the heat exchanger reaches a relatively high temperature and air passing through the heat exchanger can not absorb all the heat from the heat exchanger. This heat which is not absorbed from the heat exchanger is discharged through the chimney system or flue rather than being absorbed by the air passing over the heat exchanger and represents a significant loss in total system efficiency.
Attempts in the prior art have been made to address the problem and U.S. Pat. No. 4,485,966 discloses a pulsation device for a heating or cooling unit which is connected in series with a low voltage AC power supply, a gas valve and thermostat for a heating or cooling system. The pulsation device includes a DC (direct current) power supply, a pulsating switch connected to conduct a substantial portion of the current directed through the thermostat and gas valve of the heating unit, timer means programmed to open and close the pulsating switch according to corresponding predetermined time periods and means connected to the pulsating switch for providing a small current flow through the gas valve of the heating unit and the DC power supply when the thermostat is closed and the pulsation switch is open. The small current flow is necessary to maintain the operation of the timer means without actuating the gas valve.
The present invention provides apparatus for controlling the operation of a gas valve in a gas heating system which eliminates many of the prior art deficiencies in systems which are complicated and unreliable because of false triggering problems. Some prior art systems will not operate with electronic thermostats. Other prior art systems require separate power sources to maintain operation of the timer means during the time when the contacts of the thermostat are open.